An electron microscope image of vertically-aligned carbon-nanotube films (left) and an optical microscope image of a carbon-nanotube wafer (right). The small picture in the upper right is a 2 &times; 2cm carbon-nanotube wafer.

National Institute of Advanced Industrial Science and Technology (AIST) manufactured integrated 3D carbon-nanotube components by using single-layer carbon nanotubes. A "carbon-nanotube wafer" developed by densely aligning carbon nanotubes enabled to use microfabrication techniques of lithography.

The new technology made it possible to form any shape of electronic parts in any place. For example, AIST integrated more than a thousand 3D carbon-nanotube electronic parts on a substrate (Fig 1) and electrically drove the component.

The carbon-nanotube wafer is manufactured as follows (Fig 2). (1) A Si substrate is linearly patterned with a catalyst. (2) Carbon-nanotube films are made and vertically aligned on the Si substrate by using the "water adding CVD method" (Super Growth Method), which AIST developed in fiscal 2004.

(3) By immersing the substrate in a liquid and pulling it out, carbon-nanotube films are laid down on the substrate. (4) As the liquid dries, those carbon-nanotube films become denser and attached firmly to the substrate to form a carbon-nanotube wafer.

The carbon-nanotube film in (2) has a density of 0.03g/cc with vertically-aligned carbon nanotubes whose diameter is 2.8nm on average. The carbon-nanotube wafer made in (4), after becoming denser, is shaped like a bar with the density of 0.5g/cc.

The carbon-nanotube wafer has machine characteristics of being light and robust. At the same time, it is very pliable, and its wires do not break even when bent to more than 90°. As for the electric property, its electric resistivity is 0.008Ω·cm in the direction parallel to the alignment of the carbon nanotubes and 0.20Ω·cm in the direction vertical to the alignment, showing an anisotropy.

The carbon-nanotube wafer does not break even when a resist for photomask is applied. Therefore, it can be formed into any shape by techniques of lithography. It is also possible to form carbon-nanotube structures, such as cantilever shapes, in the chases prepared on the Si substrate.

It can be electrically driven because its carbon-nanotube structure provides a conductive property. For example, the institute fabricated and drove a carbon-nanotube relay whose electrodes are all composed of carbon nanotubes. It succeeded in mechanical switching of the carbon-nanotube cantilever by applying a voltage to gate electrodes (Fig 5).

AIST plans to evaluate the physical properties of the carbon-nanotube wafer and develop a carbon-nanotube component that takes advantage of the properties. Also, it puts emphasis on cooperation with companies and universities.

The study results announced this time was published in the online version of "Nature Nanotechnology," a science magazine in the UK May 4, 2008.